Electrochemical and in Situ Ellipsometric Investigation of the Permeability and Stability of Layered Polyelectrolyte Films

Utilization of layered polyelectrolyte films as sensor or ion-separation materials will depend critically on their stability and ion permeability in aqueous solution. We report electrochemical and in situ ellipsometric studies on the permeability and stability of poly(allylamine hydrochloride)/poly(styrenesulfonate) (PAH/PSS) and PAH/poly(acrylic acid) (PAA) films. The permeability of these layered polyelectrolyte films to Fe(CN)63- and Ru(NH3)63+ depends on the solution pH, the number of bilayers in the film, whether supporting electrolyte is present during film deposition, and the nature of constituent polycations and polyanions. Cyclic voltammetry and impedance spectroscopy show that film permeability is similar in pH 3.2- and pH 6.3-buffered solutions but increases dramatically in alkaline solutions. In situ ellipsometry helps to explain these results. Upon immersion in pH 3.2- and pH 6.3-buffered solutions, the thickness of PAH/PSS films increases by 40%, but swelling is constant over time. At pH 10,...